ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus GmbHGöttingen, Germany10.5194/acp-6-1033-2006Tropopause referenced ozone climatology and inter-annual variability (1994–2003) from the MOZAIC programmeThouretV.1CammasJ.-P.1SauvageB.1AthierG.1ZbindenR.1NédélecP.1SimonP.2KarcherF.21Laboratoire d’Aérologie, UMR 5560, Université Paul Sabatier, Toulouse, France2CNRM, Météo-France, Toulouse, France310320066410331051This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.This article is available from http://www.atmos-chem-phys.net/6/1033/2006/acp-6-1033-2006.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/6/1033/2006/acp-6-1033-2006.pdf

The MOZAIC programme collects ozone and water vapour data using automatic
equipment installed on board five long-range Airbus A340 aircraft flying
regularly all over the world since August 1994. Those measurements made
between September 1994 and August 1996 allowed the first accurate ozone
climatology at 9&ndash;12 km altitude to be generated. The seasonal variability of
the tropopause height has always provided a problem when constructing
climatologies in this region. To remove any signal from the seasonal and
synoptic scale variability in tropopause height we have chosen in this
further study of these and subsequent data to reference our climatology to
the altitude of the tropopause. We define the tropopause as a mixing zone 30 hPa
thick across the 2 pvu potential vorticity surface. A new ozone
climatology is now available for levels characteristic of the upper
troposphere (UT) and the lower stratosphere (LS) regardless of the seasonal
variations of the tropopause over the period 1994&ndash;2003. Moreover, this new
presentation has allowed an estimation of the monthly mean climatological
ozone concentration at the tropopause showing a sine seasonal variation with
a maximum in May (120 ppbv) and a minimum in November (65 ppbv). Besides, we
present a first assessment of the inter-annual variability of ozone in this
particular critical region. The overall increase in the UTLS is about
1%/yr for the 9 years sampled. However, enhanced concentrations about
10&ndash;15 % higher than the other years were recorded in 1998 and 1999 in
both the UT and the LS. This so-called "1998&ndash;1999 anomaly" may be
attributed to a combination of different processes involving large scale
modes of atmospheric variability, circulation features and local or global
pollution, but the most dominant one seems to involve the variability of the
North Atlantic Oscillation (NAO) as we find a strong positive correlation
(above 0.60) between ozone recorded in the upper troposphere and the NAO
index. A strong anti-correlation is also found between ozone and the
extremes of the Northern Annular Mode (NAM) index, attributing the lower
stratospheric variability to dynamical anomalies. Finally this analysis
highlights the coupling between the troposphere, at least the upper one, and
the stratosphere, at least the lower one.